[Patent Literature 1] JP 2010-146177 A
A technology is known where a subject vehicle obtains a relative position relation with other vehicles (i.e., target vehicles) using information transmitted from the target vehicles by vehicle-to-vehicle communication without using map information. For example, Patent Literature 1 discloses a technology as follows. A subject vehicle measures a coordinate of an own present position continuously while obtaining coordinates of positions of target vehicles by vehicle-to-vehicle communication continuously. A travel locus of a front vehicle is prepared on a virtual plane; the travel locus of the front vehicle is combined with a coordinate of a present position of another vehicle, thereby determining whether both of the front vehicle and another vehicle travel the same road.
In Patent Literature 1, a single coordinate of a present position (i.e., present position information-item) is transmitted periodically, i.e., multiple times; thereby, the preparation of the travel locus is enabled at a receiving side. Multiple present position information-items that are equivalent to a travel locus may be transmitted and received at once by vehicle-to-vehicle communication; thereby, the relative position relation between the subject vehicle and the target vehicle may be obtained only by one transmission or one reception.
All vehicles may transmit and receive multiple position information-items by vehicle-to-vehicle communication in a state where the vehicles density on road is high. In such a case, the amount of data communication increases as compared with the case where only one position information-item is transmitted and received at once; therefore, a congestion is caused in the vehicle-to-vehicle communication.